Frame Materials

Carbon fiber, or “Magic Plastic” as I like to call it. I don’t really call it that, and in reality, carbon fiber is much more than your run of the mill plastic. The fact that they build F1 car parts and airplanes out of the stuff makes it quite the versatile material. When carbon fiber was introduced as a bicycle material, it had several things going for it: it was lighter, stiffer, and soaked up road vibration/shock unlike the metal frames. On the downside, it was expensive to manufacture, and had a nasty reputation for catastrophic failure. It still has that reputation.

Another advantage of carbon fiber was the myriad of tube and frame shapes it could be made into. Carbon fiber sheets are laid in a mold similar to the fiberglass is made. Resin is then used to coat the layers, after which an internal bladder is inflated to compress the layers in the mold as the resin cures. Frames are typically made in sections then joined with more carbon fiber and resin. Hydroforming has led to more complex metal tube shapes, but the flexibility of carbon takes it further. Check out the image of the carbon fiber recumbent there. Also, carbon fiber sheets flex one way, so depending on how the sheets are laid, a tube can flex in one direction, while being rigid in the other. For example, the seat stays are vertically compliant, but are rigid sideways to offset the flex induced by hard pedaling.

After the break, I’ll go over what you need to know about carbon fiber.

When I started in the bicycle industry, at a small bike shop, in 1996, aluminum was still and “exotic” frame material. Aluminum bikes were still coming in at around the $1000 price point. My first LBS bicycle, a Trek 7000 mountain bike, was aluminum. $1100 was paid for that, and it was the entry level aluminum mountain bike.

Fast forward to 2014 and you can get an aluminum mountain bike at Target for just about $200. Granted, it is no where near the level of the Trek 7000 I bought all those years ago, but it shows that the process of making aluminum into bicycle frames has gotten a lot less expensive.

Steel is mistaken as the original material used to build the first bicycle. The first bikes were actually made of wood. Why not? It was plentiful and easy to work with. Steel came along with the high wheel bicycle.

What do you need to know about steel as a frame material? First off, it is a “soft” metal. Soft as in it is flexible. That’s why you see steel commonly used in things like springs, coil or leaf. It can flex quite a bit before failing. Don’t worry, you won’t be able to flex a steel frame to the point of failure. As such, this makes for an ideal bicycle frame because bicycles started out without suspension. The ability of steel to flex allows the frame to soak up road vibration and shock, making for a comfortable ride.

This might explain why some riders are so passionate about steel. For long distances, rough roads, in addition to a long fatigue life, a bicycle owner has a bike that could stay with him/her for quite some time. Let’s get to the nitty-gritty of this material after the break.